A wide variety of internal core lifters have been developed for use within a plastic injection mold apparatus to mold and eject plastic parts with undercuts. Most of these internal core lifters generally consist of a core blade with one end permanently mounted at a predetermined molding angle to a coupling. The coupling then slides linearly along a support mounted to the mold apparatus' ejection plate to enable the core blade to remain at the molding angle. Because the core blade is permanently attached to the coupling, these lifters commonly need to be custom designed to fit particular molds on a case by case basis.
In the plastic injection molding of plastic parts with undercuts, it is common for the molding apparatus to include an internal core lifter which when the mold is closed assists in molding the part and when the mold is opened assists in ejecting the part. The internal core lifter generally consists of a core blade with a first end designed to be incorporated in the mold cavity to mold and eject the plastic part, and an opposite end mounted to a coupling which enables the blade to pivot in a pivot plane about a single axis and translate linearly along a support normal to the pivot axis. In order for the core blade to assist in vertical ejection without damaging the undercut of the plastic part, it is commonly disposed and maintained in the molding apparatus at a mold specific molding angle, and as the mold opens, the core blade support is raised compelling the blade to move along the support, to maintain the molding angle, as its upper end moves away from the undercut to safely eject the plastic part.
The aforementioned co-pending patent application discloses a very advantageous and effective core lifter designed to readily sit at a range of molding angles in which a mold maker would desire. This core lifter substantially reduces the number of custom core lifter designs and alternative inventories because it can be cut to a desired length and can be mounted to a desired molding angle within a range desirable angles. In order to facilitate both the molding angle and horizontal travel, this core lifter has its core blade mounted at the end opposite the end configured for molding and ejecting the plastic part to a universal coupling. The universal coupling has a surface for pivotally mounting the core blade with its cooperating surface. The universal coupling also provides a surface for translating along a support in the plane which the blade may pivot for the molding angle. Thus, this core lifter effectively positions itself relatively easy to any angle in the two dimension plane needed for the molding angle and, thereby, lessening the need for costly mold apparatus particular core lifters.
The molds of molding apparatus are opened and closed with tremendous operating loads and the core lifters are subject to such loads. These operating loads are necessary to successfully open, close and seal the mold cavity and to raise and lower the core lifter and ejection means to properly and safely eject the plastic part. The core lifter disclosed in the aforementioned co-pending patent application has its core blade positioned at a given molding angle in each molding apparatus. The core blade pivots by having a curved dovetail heel at its lower end received in a curved dovetail in a universal coupling. The universal coupling travels linearly by sliding along a linear dovetail of a support. In some instances due to wear or other tolerances or load applications to the mold, the core blade may tend to cock or otherwise turn the connected universal coupling relative to the linear dovetail causing a binding of the universal coupling against its free sliding along the linear dovetail of the support. If the universal coupling should not slide along the linear dovetail of the support, the core blade then may not be raised or lowered properly during the opening and closing of the mold apparatus and, as a result, may be crushed by the mold halves causing severe damage to the core lifter and the molding apparatus.
As regards to damaging the core lifter, the core blade may deflect and, eventually, may be crushed, and because it is commonly made of metal, it may rupture in metal pieces. Because molding operations are fast, there generally is not enough warning to shut down the molding apparatus before preventing damage. The metal pieces may float freely about the molding apparatus, including the molding cavity, and cause severe scoring damage to the mold cavity, and operating surfaces of the mold apparatus and the core lifter itself. It is thus desirable to provide a core lifter having a design which takes into consideration the operating loads generated and transferred to core lifter from any direction for increasing the durability, lifetime and performance of a core lifter.
The present invention is directed toward a new and improved universal internal core lifter that allows the core blade to pivot about multiple axes to compensate for mold operating loads from any direction and, thus, preventing the core blade from twisting the universal coupling about the support which may result in severe damage.
A further object is to provide a universal internal core lifter that may be easily made to a predetermined mold apparatus length and that may easily pivot to a predetermined molding angle in a range of molding angles.
A further object is to have a universal internal core lifter that is highly durable and efficient to manufacture and use. These and other objects will become apparent from the following detailed description and the appended claims.